I. Field of the Invention
The present invention relates generally to fluid flow meters and, more particularly, to a fluid flow meter in which the fluid flow range for the flow meter can be easily varied.
II. Description of the Prior Art
There have been a number of previously known fluid flow meters having a housing with a fluid inlet, a fluid outlet and means for measuring and visually indicating the fluid flow rate through the flow meter. For example, in one type of previously known fluid flow meter, a semicircular vane cooperates with a hemispherical shaped housing disposed between the fluid inlet and the fluid outlet. Rotation of the vane provides a variable size opening between the vane edge and the housing while resilient means urge the vane toward a closed position. An indicator assembly measures the rotation of the vane caused by the fluid flow through the housing to provide an exteriorly visible signal of the fluid flow rate through the housing.
In a still further type of fluid flow meter, a tapered needle cooperates with a port which fluidly connects the inlet to the outlet. In addition, a piston is axially slidably mounted within the housing so that the displacement of the piston caused by the fluid flow through the flow meter variably opens the port in dependence upon the flow rate. Electrical and/or mechanical indicating means are attached to the piston to provide a signal of the axial displacement or position of the piston and, hence, of the flow rate through the flow meter.
One disadvantage of these previously known flow meters is that the flow range for the flow meter is preset and nonadjustable after assembly of the flow meter. Consequently, if a different range for the flow meter is desired, it is necessary to replace the entire flow meter.
A still further disadvantage of the previously known flow meters with movable pistons is that the pistons tend to cock during travel which produces inaccurate flow meter readings. Large seals can be provided on opposite ends of the piston to minimize cocking but large seals increase the friction or drag between the piston and the housing and also adversely effect the accuracy and reliability of the flow meter.